This invention relates to a method for analyzing the seasonal growing conditions of crops by use of infrared aerial photography. Infrared aerial photography has been used to detect the presence and amount of growing crops. Infrared photographs are also useful in the identification of field areas subject to disease or other traumatic conditions. However, the present method carries such analysis into a time related process, by which the growing conditions of a crop can be compared from one day or week to the next with accuracy, and by which conditions in various fields can be compared accurately. Furthermore, the current growing conditions of a crop can be accurately compared to optimum conditions derived experientially from analyses of earlier growing seasons.
The analyses of crop condition is accomplished by using infrared aerial photographs of the total field area and projecting the resulting false color transparencies onto a color averager for reception by a color analyzer. The color values measured by the analyzers are segregated for three colors, (red, blue and green) and are corrected for exposure variations resulting from photographic, weather and time factors. The resulting color values can then be plotted for each field, and compared to plotted values representative of optimum growing conditions.
My first efforts in taking infrared aerial photographs of crops showed to me that there were substantial difficulties involved in normal methods used by me and others in this industry. The primary problem was that one week the slide of the subject field would appear to be one color, and the next week it would appear somewhat different in color, although I was sure that the color shift had not occurred in the field. This difference in the visual color perception of the slides resulted from five basic considerations: (a) each film batch was somewhat different, (b) colors changed depending upon whether the photograph was taken on an overcast day or not, (c) color changed with the time of day and date, (d) slight differences in exposure of the film would change color relationships, (e) color shift problems also were due to processing variations in handling the film.
To overcome the difficulties involved in visually analyzing slides of a field, I have developed a method for using an electronic color analyzer and resulting graph of the color density numbers. To provide continuity from one photograph to the next, I computed a number of corrections relating to the five basic problems related above. These corrections are applied to the analyzer readings prior to charting. The electronic color analyzer has the further ability to detect color shifts below the visual perception level, and provides substantially greater accuracy in the end result as charted.
To check this method, I have kept careful records of flight data, used color standards and other information and have plotted corrected colors from these readings each week during entire growing seasons for various crops. I then checked yield data from the analyzed fields and found that those crops which followed particular color trends through the season produced good harvests and those that deviated from these trends did not. By refining this analysis of color value trends, I have found that I can determine approximate yield of a field, quality of the crop, high or low nitrogen levels, and whole field stresses that were impossible to identify with prior infrared aerial photography techniques. It is important to note that the electronic analysis of these photographs cannot be used except in conjunction with normal visual field inspections and organic chemical crop and soil analysis. When used in this manner, the infrared aerial photography processes and electronic color analyses fill in information that is missing in agronometrical testing methods and previous methods of visual infrared photographic analyses.